While no-one believed human hands to be autoclave-level sterile, a study from the University of Colorado at Boulder makes surprising reading.

Researcher Noah Fierer found an average hand has around 150 species of bacteria living on it, with women having more than men, as reported in PNAS (link should go live soon). In addition, Fierer’s research team found over 4,700 species over 51 people and only five species were shared by all those in their study.

“The sheer number of bacteria species detected on the hands of the study participants was a big surprise, and so was the greater diversity of bacteria we found on the hands of women,” says Fierer (press release, LA Times). “The findings don’t necessarily mean that women have more germs than men, just more variety.”

Before you start scrubbing your hands till they bleed, this is not a unhealthy thing. In fact, says Fierer, knowing what normal levels of bacteria are helps establish a baseline, which might help detect differences in bacterial makeup in unhealthy people.

Washing doesn’t do much, the team notes in their paper:

Either the bacterial colonies rapidly re-establish after hand washing, or washing (as practiced by the students included in this study) does not remove the majority of bacteria taxa found on the skin surface.

This obviously leaves open the possibility that undergraduates at CU have poor personal hygiene.

AP adds:

Asked if guys should worry about holding hands with girls, [co-author Rob] Knight said: “I guess it depends on which girl.”

Image: Punchstock